ENSTROM F-28F/280F SERIES MAINTENANCE MANUAL SUPPLEMENT
Rev.
5
MM-21-11
Nov
5/13
21-7. Hi/Lo Rotor RPM Warning System
The Hi/Lo Rotor RPM Warning System consists of the P/N ECD4079-1 Hi/Lo Rotor RPM
switch (signal conditioning unit), a ROTOR RPM warning light, a magnetic sensor,
microswitches (S19 and S24), a lamp test switch (S25), warning horn, and a warning tone
generator interfaced with the audio panel. The magnetic sensor, located in the forward
portion of the main rotor transmission housing, is positioned to sense the passage of the
ring gear teeth. A signal is sent to the signal conditioning unit, which activates the ROTOR
RPM warning light on the annunciator panel, an audible warning horn, and a tone in the
audio system headsets when the main rotor rpm is below 332 RPM or above 385 RPM. The
signal conditioning unit is also activated by switch (S24) on the clutch actuator mechanism.
The ROTOR RPM warning light, horn, and tone will be on when the CLUTCH ENGAGE
light is out, and the main rotor rpm is below 332 RPM or above 385 RPM. A microswitch
(S19), located on the collective torque tube behind the pilot’s seat, deactivates the warning
horn and tone when the collective controls are on the down stop. The annunciator panel
press-to-test switch (S25) will illuminate the ROTOR RPM warning light for test purposes
when the switch (S25) is pressed.
A.
Signal Conditioning Unit
The signal conditioning unit, located behind the passenger’s back cushion, reads the signal
from the magnetic pickup and activates the ROTOR RPM warning light, and audio horn and
tone. The wiring schematic diagram of the Hi/Lo Rotor RPM Warning System is detailed in
Diagram 21-5 Sheet 3.
B.
Removal – Signal Conditioning Unit
(1)
Ensure all electrical power is off.
(2)
Remove the back cushions and seatback access panel.
(3)
Unplug the electrical connector from the signal conditioning unit.
(4)
Remove the four screws mounting the signal conditioning unit to the bulkhead.
(5)
Remove the signal conditioning unit.
C.
Inspection – Signal Conditioning Unit
(1)
Inspect the signal conditioning unit for damage, security of installation, and proper
operation.
D.
Repair – Signal Conditioning Unit
(1)
Replace the signal conditioning unit if damaged or the unit fails to activate the light
and horn or the unit cannot be set to activate at rotor speeds below 332 RPM and
above 385 RPM.
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